Most automotive vehicles are propelled by internal combustion engines consuming hydrocarbon fuels. Burning these fuels produces exhaust gas containing harmful air-pollutants, such as carbon monoxide, nitrogen oxides, and unburned hydrocarbons. It also contains substantial amount of carbon dioxide which, if produced in large quantities worldwide over long period of time, can contribute to an undesirable increase in average global temperature. Concern for clean air and a desire to prevent adverse consequences of man-made global warming dictate a need to substantially improve fuel efficiency of automotive vehicles.
By itself, the internal combustion engine is a reasonably efficient machine. Unfortunately, the driving pattern of most automotive vehicles is such, that a substantial fraction of energy produced by their engines is wasted. Typically, the driving pattern involves frequent accelerations, each followed by a deceleration. Each acceleration involves a significant increase in fuel consumption needed to produce the additional energy necessary to increase the vehicle speed. Then, during a subsequent deceleration, this added energy is absorbed by vehicle brakes and dissipated as heat.
Attempts to overcome such waste of energy led to development of systems in which the energy of vehicle motion is not dissipated during braking, but converted into a form in which it can be temporarily stored and, then, used again to accelerate the vehicle at a later time. Typically, such system includes an internal combustion engine, an energy storage, and a second propulsion system that absorbs the energy of vehicle motion and deposits it into the storage during braking. During subsequent acceleration, the second propulsion system receives energy from the energy storage and uses it to supplement the work of the internal combustion engine. Such systems are known as hybrid vehicle systems. An electric hybrid includes an electric generator/motor as a second propulsion system, and an electric battery for energy storage. A fluid-power hybrid includes a pump/motor and a pressurized-fluid accumulator. A flywheel hybrid includes a variable-ratio transmission and a flywheel.
Air hybrid differs from most other hybrid systems in that it does not require a second propulsion system. Instead, the vehicle engine performs both absorption and recovery of braking energy, using compressed air for energy storage and, later, for compressed-air assist. Elimination of the need for a second propulsion system leads to a substantial reduction in cost and complexity of the hybrid system.
An air-hybrid system can substantially reduce the vehicle fuel consumption during braking and acceleration. There is, however, no improvement when the vehicle is cruising with approximately constant speed, because the compressed air accumulated during braking is completely spent for compressed-air assist during subsequent acceleration. Much greater fuel economy benefit could be achieved if compressed-air assist were available during both acceleration and cruise. This can be accomplished by providing the vehicle with an auxiliary reservoir filled with compressed air that can be used for compressed-air assist when compressed air accumulated during braking is not available. Such auxiliary reservoir can be periodically recharged with compressed air by using an outside source of energy when the vehicle is not in motion.
Typically, such system can use an electrically-driven on-board compressor that can be connected to an outside source of electric power when the vehicle is parked in the owner's garage or elsewhere. In this way, electric power from an electric grid is indirectly used for air-hybrid vehicle propulsion replacing some of the hydrocarbon fuel. This is the concept of the plug-in air hybrid. Since electric power is substantially less expensive than the hydrocarbon fuel it replaces, using the plug-in air hybrid for vehicle propulsion provides substantial operational cost savings to the vehicle owner. It also reduces the amount of harmful exhaust pollutants associated with hydrocarbon fuel combustion.
A plug-in air-hybrid system that combines the concept of saving the vehicle braking energy as compressed air and using it for subsequent compressed-air assist with the concept of an additional compressed-air assist provided by an on-board rechargeable compressed-air reservoir using an outside source of energy for its periodic recharging with compressed air is the subject of the present invention.